Keyboard: Port of TMK XT USB Converter (#3619)

* Converter: add XT USB converter from TMK

* Converter: port TMK code for USB converter to QMK

* Apply requested changes after code review by @drashna

- use "pragma once" instead of include guards
- use LAYOUT instead of KEYMAP
- allow customisation with matrix_init_user() and matrix_scan_user()
- set BOOTLOADER instead of BOOTLOADER_SIZE
- Add XT_ENABLE to OPT_DEFS

* Remove unnecessary lines

3 files changed, 249 insertions, 0 deletions

diff --git a/tmk_core/protocol.mk b/tmk_core/protocol.mk
index 54913329e..78b9deb29 100644
--- a/tmk_core/protocol.mk
+++ b/tmk_core/protocol.mk
@@ -50,5 +50,10 @@ ifdef ADB_MOUSE_ENABLE
          OPT_DEFS += -DADB_MOUSE_ENABLE -DMOUSE_ENABLE
 endif
 
+ifdef XT_ENABLE
+  SRC += $(PROTOCOL_DIR)/xt_interrupt.c
+  OPT_DEFS += -DXT_ENABLE
+endif
+
 # Search Path
 VPATH += $(TMK_DIR)/protocol
diff --git a/tmk_core/protocol/xt.h b/tmk_core/protocol/xt.h
new file mode 100644
index 000000000..93bc5daf8
--- /dev/null
+++ b/tmk_core/protocol/xt.h
@@ -0,0 +1,71 @@
+/*
+Copyright 2018 Jun WAKO <wakojun@gmail.com>
+Copyright 2016 Ethan Apodaca <papodaca@gmail.com>
+
+This software is licensed with a Modified BSD License.
+All of this is supposed to be Free Software, Open Source, DFSG-free,
+GPL-compatible, and OK to use in both free and proprietary applications.
+Additions and corrections to this file are welcome.
+
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright
+  notice, this list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright
+  notice, this list of conditions and the following disclaimer in
+  the documentation and/or other materials provided with the
+  distribution.
+
+* Neither the name of the copyright holders nor the names of
+  contributors may be used to endorse or promote products derived
+  from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#ifndef XT_H
+#define XT_H
+
+#define XT_DATA_IN()        do { \
+    XT_DATA_DDR  &= ~(1<<XT_DATA_BIT); \
+    XT_DATA_PORT |=  (1<<XT_DATA_BIT); \
+} while (0)
+
+#define XT_DATA_READ()      (XT_DATA_PIN&(1<<XT_DATA_BIT))
+
+#define XT_DATA_LO()        do { \
+    XT_DATA_PORT &= ~(1<<XT_DATA_BIT); \
+    XT_DATA_DDR  |=  (1<<XT_DATA_BIT); \
+} while (0)
+
+
+#define XT_CLOCK_IN()       do { \
+    XT_CLOCK_DDR  &= ~(1<<XT_CLOCK_BIT); \
+    XT_CLOCK_PORT |=  (1<<XT_CLOCK_BIT); \
+} while (0)
+
+#define XT_CLOCK_READ()     (XT_CLOCK_PIN&(1<<XT_CLOCK_BIT))
+
+#define XT_CLOCK_LO()       do { \
+    XT_CLOCK_PORT &= ~(1<<XT_CLOCK_BIT); \
+    XT_CLOCK_DDR  |=  (1<<XT_CLOCK_BIT); \
+} while (0)
+
+
+void xt_host_init(void);
+uint8_t xt_host_recv(void);
+
+#endif
diff --git a/tmk_core/protocol/xt_interrupt.c b/tmk_core/protocol/xt_interrupt.c
new file mode 100644
index 000000000..3823bbd3a
--- /dev/null
+++ b/tmk_core/protocol/xt_interrupt.c
@@ -0,0 +1,173 @@
+/*
+Copyright 2018 Jun WAKO <wakojun@gmail.com>
+Copyright 2016 Ethan Apodaca <papodaca@gmail.com>
+
+This software is licensed with a Modified BSD License.
+All of this is supposed to be Free Software, Open Source, DFSG-free,
+GPL-compatible, and OK to use in both free and proprietary applications.
+Additions and corrections to this file are welcome.
+
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright
+  notice, this list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright
+  notice, this list of conditions and the following disclaimer in
+  the documentation and/or other materials provided with the
+  distribution.
+
+* Neither the name of the copyright holders nor the names of
+  contributors may be used to endorse or promote products derived
+  from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#include <stdbool.h>
+#include <avr/interrupt.h>
+#include <util/delay.h>
+#include "xt.h"
+#include "wait.h"
+#include "print.h"
+
+static inline uint8_t pbuf_dequeue(void);
+static inline void pbuf_enqueue(uint8_t data);
+static inline bool pbuf_has_data(void);
+static inline void pbuf_clear(void);
+
+void xt_host_init(void)
+{
+    XT_INT_INIT();
+    XT_INT_OFF();
+
+    /* hard reset */
+#ifdef XT_RESET
+    XT_RESET();
+#endif
+
+    /* soft reset: pull clock line down for 20ms */
+    XT_DATA_LO();
+    XT_CLOCK_LO();
+    _delay_ms(20);
+
+    /* input mode with pullup */
+    XT_CLOCK_IN();
+    XT_DATA_IN();
+
+    XT_INT_ON();
+}
+
+/* get data received by interrupt */
+uint8_t xt_host_recv(void)
+{
+    if (pbuf_has_data()) {
+        return pbuf_dequeue();
+    } else {
+        return 0;
+    }
+}
+
+ISR(XT_INT_VECT)
+{
+    /*
+     * XT signal format consits of 10 or 9 clocks and sends start bits and 8-bit data,
+     * which should be read on falling edge of clock.
+     *
+     *  start(0), start(1), bit0, bit1, bit2, bit3, bit4, bit5, bit6, bit7
+     *
+     * Original IBM XT keyboard sends start(0) bit while some of clones don't.
+     * Start(0) bit is read as low on data line while start(1) as high.
+     *
+     * https://github.com/tmk/tmk_keyboard/wiki/IBM-PC-XT-Keyboard-Protocol
+     */
+    static enum {
+        START, BIT0, BIT1, BIT2, BIT3, BIT4, BIT5, BIT6, BIT7
+    } state = START;
+    static uint8_t data = 0;
+
+    uint8_t dbit = XT_DATA_READ();
+
+    // This is needed if using PCINT which can be called on both falling and rising edge
+    //if (XT_CLOCK_READ()) return;
+
+    switch (state) {
+        case START:
+            // ignore start(0) bit
+            if (!dbit) return;
+            break;
+        case BIT0 ... BIT7:
+            data >>= 1;
+            if (dbit)
+                data |= 0x80;
+            break;
+    }
+    if (state++ == BIT7) {
+        pbuf_enqueue(data);
+        state = START;
+        data = 0;
+    }
+    return;
+}
+
+/*--------------------------------------------------------------------
+ * Ring buffer to store scan codes from keyboard
+ *------------------------------------------------------------------*/
+#define PBUF_SIZE 32
+static uint8_t pbuf[PBUF_SIZE];
+static uint8_t pbuf_head = 0;
+static uint8_t pbuf_tail = 0;
+static inline void pbuf_enqueue(uint8_t data)
+{
+    uint8_t sreg = SREG;
+    cli();
+    uint8_t next = (pbuf_head + 1) % PBUF_SIZE;
+    if (next != pbuf_tail) {
+        pbuf[pbuf_head] = data;
+        pbuf_head = next;
+    } else {
+        print("pbuf: full\n");
+    }
+    SREG = sreg;
+}
+static inline uint8_t pbuf_dequeue(void)
+{
+    uint8_t val = 0;
+
+    uint8_t sreg = SREG;
+    cli();
+    if (pbuf_head != pbuf_tail) {
+        val = pbuf[pbuf_tail];
+        pbuf_tail = (pbuf_tail + 1) % PBUF_SIZE;
+    }
+    SREG = sreg;
+
+    return val;
+}
+static inline bool pbuf_has_data(void)
+{
+    uint8_t sreg = SREG;
+    cli();
+    bool has_data = (pbuf_head != pbuf_tail);
+    SREG = sreg;
+    return has_data;
+}
+static inline void pbuf_clear(void)
+{
+    uint8_t sreg = SREG;
+    cli();
+    pbuf_head = pbuf_tail = 0;
+    SREG = sreg;
+}